Discovery 1 temp gauge

Hi all I wonder if someone can help me. If I go for a drive and get to operating temperature randomly my temp gauge will rise up to the red. Then goes up and down when I turn heater on and off or turn headlights on or basically just use any auxiliary electrics. All of the trucks lights also dim when the gauge rises at night. But as soon as I stop and let it tick over parked it’s fine. Slowly driving me insane

My guess will be bad earth strap from engine to chassis. When you apply the handbrake it earths through the cable which is why its ok then

My guess is bad earth strap. When you put the handbrake on it earths through the cable which is why its ok when parked

Kev12 said:

My guess is bad earth strap. When you put the handbrake on it earths through the cable which is why its ok when parked

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I cleaned engine too chassis earth and I also fitted another one on the other side to be sure. Also I tried earlier and doesn’t make a difference with handbrake off when I stopped